1. Field of the Invention
The present invention relates to a hot water supply apparatus having an instantaneous hot water supply function.
2. Background of the Related Art
A conventional hot water supply apparatus having an instantaneous hot water supply function is provided with: a water heater having a burner and a heat exchanger for supplying hot water heated by combustion by the burner; a cold water supply pipe for introducing cold water from a cold water supply source into a cold water inlet of the heat exchanger; a hot water delivery pipe connected to a hot water outlet of the heat exchanger so as to introduce the hot water heated by the heat exchanger to a hot water supply terminal; a bypass pipe for introducing hot water from that portion of the hot water delivery pipe which is in the neighborhood of the hot water supply terminal into the cold water supply pipe; and a circulation pump interposed in the bypass pipe. By the operation of the circulation pump, the water is arranged to be circulated in a circulation path from the hot water outlet of the heat exchanger, the bypass pipe, the cold water supply pipe, back to the cold water inlet of the heat exchanger (see, e.g., JP-2011-247487A). Then by performing the instantaneous hot water supply operation in which the circulation pump is in operation and also the burner is in combustion, water circulation takes place in the circulation path while heating the water in the heat exchanger, whereby upon receipt of a request for hot water delivery, hot water at an appropriate temperature is arranged to be supplied with a good response to the hot water supply terminal. Further, according to this arrangement, during the instantaneous hot water supply operation, when the combustion by the burner has continued for a certain predetermined period of time, or when the hot water delivery temperature has exceeded a predetermined temperature, the instantaneous hot water supply operation is finished. (Note: In this specification, the expression of “that . . . which” e.g., “that portion of the hot water delivery pipe which is in the neighborhood of . . . ” shall be understood to be equal in meaning to “such a portion of the hot water delivery pipe as is in the neighborhood of . . . ”)
By the way, in case a mixing faucet (hot and cold water mixing valve) is used as the hot water supply terminal, the hot water delivery pipe is connected to a hot water inlet of the mixing faucet, and a cold water delivery pipe branched from the cold water supply pipe is connected to a cold water inlet of the mixing faucet. In this arrangement, the piping cost will become expensive if the bypass pipe must be provided to connect that portion of the hot water delivery pipe which is in the neighborhood of the mixing faucet to the cold water supply pipe, in addition to the cold water delivery pipe which extends to the mixing faucet that is located away from the water heater.
As a solution, there is also considered a conventional hot water supply apparatus provided with: a thermo-sensitive valve connected, in the neighborhood of the mixing faucet, to the cold water delivery pipe and to the hot water delivery pipe in parallel to the mixing faucet; a circulation pump parallelly connected to that portion of the cold water supply pipe which is on a downstream side of the branch of the cold water delivery pipe from the cold water supply pipe; and a return pipe for introducing, into a pump suction port of the circulation pump, the hot water from that portion of the hot water delivery pipe which is on the upstream side of the thermo-sensitive valve. The thermo-sensitive valve is arranged to be opened to bring the cold water delivery pipe into communication with the hot water delivery pipe when the temperature of the hot water to flow inside the thermo-sensitive valve is below a predetermined temperature, and to be closed to shut off the communication between the cold water delivery pipe and the hot water delivery pipe when the temperature of the hot water to flow inside the thermo-sensitive valve is above the predetermined temperature. It is thus so arranged that, by the operation of the circulation pump, water circulation takes place in a first circulation path from the hot water outlet of the heat exchanger through the return pipe, the circulation pump, and the cold water supply pipe back into the cold water inlet of the heat exchanger and, at the same time, when the thermo-sensitive valve is opened, water circulation takes place also in a second circulation path from the hot water outlet of the heat exchanger through the hot water delivery pipe, the thermo-sensitive valve, the cold water delivery pipe, the circulation pump, and the cold water supply pipe back to the cold water inlet of the heat exchanger. According to this arrangement, at the time of performing instantaneous hot water supply operation in which the circulation pump is in operation and also the burner is in combustion, it is possible to circulate the cold water in the second circulation path while heating it by the heat exchanger, thereby keeping the heated hot water supplied up to the neighborhood of the mixing faucet. As a consequence, it is not necessary to provide the apparatus with the above-described bypass pipe, thereby reducing the piping costs.
In this arrangement, however, if the instantaneous hot water supply operation is finished when the combustion by the burner has continued for a predetermined period of time during the instantaneous hot water supply operation, or when the hot water delivery temperature has exceeded a predetermined temperature during the instantaneous hot water supply operation, the following disadvantages will occur. In other words, the length of piping from the water heater to the mixing faucet varies from site of one installation to site of another installation. Therefore, if the instantaneous hot water supply operation is finished when the combustion has continued for a predetermined period of time, the temperature of the circulated water, in case of a long piping length, will not rise sufficiently at the time of finishing the instantaneous hot water supply operation. In case of a short piping length, on the other hand, the temperature of the circulated water will be excessively high at the time of finishing the instantaneous hot water supply operation. In this manner, the instantaneous hot water supply operation becomes too much or too little in operation. In addition, the hot water delivery temperature is detected by a hot water delivery temperature sensor for detecting the hot water temperature in the hot water delivery pipe disposed in the water heater. Therefore, before the temperature of the water in the neighborhood of the mixing faucet that is far from the water heater has been elevated sufficiently, the temperature as detected by the hot water delivery temperature sensor will be above the predetermined temperature, whereby the instantaneous hot water supply operation will be finished. As a result, the instantaneous hot water supply operation will result in a shortage of operation.